Substrate potential of last interglacial to Holocene permafrost organic matter for future microbial greenhouse gas production

Abstract

Abstract. In this study the organic matter (OM) in several permafrost cores from Bol'shoy Lyakhovsky Island in NE Siberia was investigated. In the context of the observed global warming the aim was to evaluate the potential of freeze-locked OM from different depositional ages to act as a substrate provider for microbial production of greenhouse gases from thawing permafrost. To assess this potential, the concentrations of free and bound acetate, which form an appropriate substrate for methanogenesis, were determined. The largest free-acetate (in pore water) and bound-acetate (organic-matrix-linked) substrate pools were present in interstadial marine isotope stage (MIS) 3 and stadial MIS 4 Yedoma permafrost deposits. In contrast, deposits from the last interglacial MIS 5e (Eemian) contained only a small pool of substrates. The Holocene (MIS 1) deposits revealed a significant bound-acetate pool, representing a future substrate potential upon release during OM degradation. Additionally, pyrolysis experiments on the OM allocated an increased aliphatic character to the MIS 3 and 4 Late Pleistocene deposits, which might indicate less decomposed and presumably more easily degradable OM. Biomarkers for past microbial communities, including those for methanogenic archaea, also showed the highest abundance during MIS 3 and 4, which indicated OM-stimulated microbial degradation and presumably greenhouse gas production during time of deposition. On a broader perspective, Arctic warming will increase and deepen permafrost thaw and favor substrate availability from older freeze-locked permafrost deposits. Thus, the Yedoma deposits especially showed a high potential for providing substrates relevant for microbial greenhouse gas production.

Greenhouse gas production in degrading ice-rich permafrost deposits in northeastern Siberia

“…However, owing to the high ice content, yedoma deposits are highly susceptible to warming-induced environmental changes, erosion, and ground subsidence following permafrost thaw (e.g., Morgenstern et al, 2013). Only 30 % of the yedoma region (about 416 000 km 2 ) is considered intact, while the other 70 % has already undergone some level of permafrost degradation (Strauss et al, 2013). Today, the whole yedoma domain stores 213-456 Pg of OC, of which 83-269 Pg is stored in intact yedoma and 169-240 Pg in thermokarst and refrozen taberal deposits (Zimov et al, 2006;Strauss et al, 2013Strauss et al, , 2017Hugelius et al, 2014;Walter Anthony et al, 2014).…”

“…Only 30 % of the yedoma region (about 416 000 km 2 ) is considered intact, while the other 70 % has already undergone some level of permafrost degradation (Strauss et al, 2013). Today, the whole yedoma domain stores 213-456 Pg of OC, of which 83-269 Pg is stored in intact yedoma and 169-240 Pg in thermokarst and refrozen taberal deposits (Zimov et al, 2006;Strauss et al, 2013Strauss et al, , 2017Hugelius et al, 2014;Walter Anthony et al, 2014). For an about 88 000 km 2 area along the Bolshaya Chukochya and Alazeya River basins and the eastern parts of the Yana-Indigirka and Kolyma lowlands in northeastern Siberia, Shmelev et al (2017) estimate the size of the total carbon pool in the upper 25 m to be 31.2 Pg, of which 3.7 Pg is stored in yedoma deposits.…”

n-Alkane Characteristics of Thawed Permafrost Deposits Below a Thermokarst Lake on Bykovsky Peninsula, Northeastern Siberia

“…Previous permafrost research on the Bykovsky Peninsula included cryostratigraphical and cryolithological research on Yedoma and thermokarst-affected deposits (Kunitsky, 1989;Slagoda, 1993;Schirrmeister et al, 2002aSchirrmeister et al, ,b, 2018Slagoda, 2004Slagoda, , 2005Grosse et al, 2007;Romankevich et al, 2017;Ulyantsev et al, 2017). The total organic carbon (TOC) content of Yedoma deposits on the east coast of the Bykovsky Peninsula (Mamontovy Khayata) ranges from 2 to 14 wt%, whereas Holocene cover deposits on top of the Yedoma have a TOC between 2 and 27 wt% (Schirrmeister et al, 2002a).…”

“…A first estimate of the taberal deposit OC pools suggests ∼114 Gt OC, which is about 25% of the Yedoma domain OC storage (∼398 Gt) (Walter Anthony et al, 2014;Strauss et al, 2017). In several studies, it is also shown that the OM degradability in Yedoma deposits is higher compared to that in Holocene deposits (Knoblauch et al, 2013;Strauss et al, 2015;Jongejans et al, 2018;Stapel et al, 2018). However, the fate of OM in Yedoma deposits affected by thawing and subsequent qualitative and quantitative changes is poorly understood.…”

“…The study of the biomolecules and other OM characteristics can give important insights into OM degradability and could hence greatly improve estimates of permafrost OM mobilization (Andersson and Meyers, 2012;Sánchez-García et al, 2014). A few studies have previously focused on molecular biomarkers in northeastern Siberian permafrost deposits (Zech et al, 2010;Höfle et al, 2013;Strauss et al, 2015;Stapel et al, 2018). In general, the abundance and distribution of n-alkanes, which are long-chained, single bonded hydrocarbons, are used as indicator for OM characterization.…”